Where I live, it’s too warm out for a white Christmas. But in the deep ocean, it’s always snowing. I’m talking about marine snow, or flakes of biological debris like dirt, dead phytoplankton and algae, and even bits of faecal matter that shower down from higher waters. So festive!
As off-putting as this snow may sound, it serves an important purpose in regulating the climate and providing nutrients that life on the seafloor needs to thrive. To get a better grip on the detritus, 20 Australian scientists from the Institute for Marine and Antarctic Studies and several universities are sending ocean robots into the Southern Ocean to learn more about this bizarre but crucial process.
The dead stuff marine snow is made of is largely carbon-based, and when it falls to the bottom of the ocean, it essentially sequesters carbon that would otherwise be in the atmosphere as carbon dioxide. Data show that the material traps hundreds of millions of tons of the globe-warming compound every year. Marine snow is also a huge source of nutrients that otherwise wouldn’t be available on the bottom of the sea. Without it, life on the land and the seafloor would look a lot different.
This month, the team boarded a research vessel in Hobart, Tasmania to deploy the robots, which have been fitted with probes to track and monitor how biological matter decomposes, becomes snow, and floats down into the ocean’s depths. They also sent down sediment traps to measure how much exactly how much carbon marine snow in the Southern Ocean captures today, and what factors lead it to capture more or less of the greenhouse gas on the surface.
“During the voyage, we will deploy a fleet of deep-diving robotic floats and gliders that use new bio-optical sensors to ‘photograph’ the density of the algae at different depths,” Philip Boyd, a professor of marine biogeochemistry at the University of Tasmania and the voyage’s chief scientist, said in a statement.“When they return to the ocean surface, these floats will immediately transmit their data back to us via satellite.”
It will be the first marine snow-focused voyage to combine human observations from a ship with deep-diving robots and gliders, and satellite technology.
“It’s a bit like an astronomer who has only been able to study one star at a time suddenly being able to observe the galaxy in three-dimensions,” Boyd said.
Patricia Yager, a professor of marine science at the University of Georgia who isn’t part of the project, said she’s excitedly anticipating the voyage’s results.
“People have been measuring marine snow for a very long time,” she said. “What we haven’t had until now is all these nifty new robotic tools…and ways of measuring it to a much much greater degree than we ever could have in the past. Hitting it with a battery of all the tools that we now have as oceanographers is really impressive.”
She also said the research is coming at an important time, because it could help shed light on how marine snow production is changing due to the warming climate. Research shows that the oceans have steadily been producing more marine snow — and thereby sequestering more and more carbon — over the past 50 years even as the Earth has gotten hotter.
But in the future, as the planet keeps warming, that may change. When surface waters heat up, they can have a harder time mixing with cooler waters down below, since warmer water is less dense than colder water. That can make it harder for debris to sink down to the deep sea. Studies also indicate that oceans, including the Southern Ocean, have seen a decrease in phytoplankton due to a mix of hotter temperatures and acidification as water absorbs excess carbon dioxide from human activities. That’s important for the fate of marine snow; part of why the material is so nutrient-rich is that those tiny creatures use energy from sunlight to take in carbon, nitrogen, and other materials from life in the ocean. With less compound-rich phytoplankton around to turn into marine snow, the oceans could sequester less carbon and endanger life on the fragile seafloor.
“What we don’t know very well is how the marine snow is going to work in the current state of climate change, whether the efficiency of [carbon sequestration] is going to go up with climate change, which would help us out, or if the efficiency is going to go down, which would be a big problem,” Yager said. “It’s one of the key questions of our time.”
If you’re missing the snow this holiday season, you can check out the researchers’ voyage blog where they’re documenting their trip.